Electrochemical gas sensors are generally known. They usually have a plurality of electrodes, which are in conductive contact with an electrolyte liquid and form in this way a galvanic cell, hereinafter also called electrochemical measuring cell. There are both sensors that are used stationarily and sensors that are used in portable devices.
The industrial field of application of such sensors ranges, for example, from the chemical industry to the monitoring of refrigerating plants up to agricultural plants. The sensors are used especially to detect critical concentrations and flammable and/or toxic gases in time and to warn against a corresponding hazard. In many areas of the chemical industry, just as in the semiconductor industry, especially the detection of so-called sour gases is of great interest in this connection in order to guarantee safety at the workplace. Sour gases are generally defined in the sense of the present invention as gases that form (weak) acids, for example, halogen halides, such as HF and HCl, hydrogen sulfide or even acetic acid, when dissolved in water.
GB 2129562 B discloses in this connection the electrochemical detection of hydrogen fluoride (HF). Both the cathode and the anode of the sensor proposed there are platinum wires. A mixture of calcium bromide and calcium bromate is used as the electrolyte. However, this detection method is especially flow- and temperature-dependent.
An alternative solution is known from WO 2002/031485 A1. A measuring electrode consisting of an electrochemically active metal oxide powder is proposed here. However, such metal oxide powders may have high cross-sensitivities to other gases, as a result of which low concentrations of the target gas cannot always be detected reliably.
WO 1999/001758 A1 also discloses an electrochemical sensor, which is said to be used especially to detect hydrogen chloride. The working electrode in this sensor has an electrochemically active surface consisting of gold. However, this is dissolved over time, which may lead to the failure of the sensor in an emergency.